The present invention relates to improvements in compressors or their component parts and particularly to flooded compressor systems employing screw rotors or similar inter-engaging rotating parts to effect compression of a gas.
Systems of the aforementioned kind conventionally comprise a number of major component parts including a compressor unit including inter-engaging rotors adapted to receive the gas (normally air) to be compressed through an inlet filter and a main throttle valve. Lubricating oil for the rotors is also introduced into the compressor unit adjacent its inlet zone and a mixture of compressed gas and oil is discharged from this unit to be separated in a separator vessel. Oil collected in the separator vessel is returned via an oil filter and an oil cooler to the compressor unit inlet zone and clean compressed gas is discharged usually to a receiving vessel from which it is withdrawn as desired by an end user. The discharged compressed gas is normally passed through a coalescent type final filter to remove any remaining fine oil droplets. This filter element is commonly housed within the main separator vessel or within an extension of the main separator vessel manufactured for the purpose of containing the filter element. Problems associated with this conventional positioning of the filter element are discussed in European Patent No. 0,121,999. There are a number of difficulties associated with conventional arrangements of compressor systems of the aforementioned kind. These include the physical size of the system which may include two relatively large pressure tanks, one acting as the separator vessel and the other forming the clean gas receiving vessel. A further problem is associated with the oil cooler which commonly comprises a pair of header manifolds interconnected by a plurality of finned heat exchange tubes through which the oil must pass after being discharged from the separator vessel. A still further problem with conventional arrangements is the number of pipes or lines that must be used to interconnect various component parts in the system and more particularly the number of fluid tight joints, (many operating under high pressure conditions) that need to be formed and then checked for operational performance during manufacture of such systems. Generally speaking it is considered highly desirable to reduce the inventory of parts needed in such systems which has beneficial effects both on material costs and labour costs in the manufacturing process.
U.S. Pat. No. 4,668,252 to Alfred Gerdau filed on the 13th June, 1985, discloses a separator for compressor systems of the aforementioned type wherein the vessel of the separator is not a large pressure tank but rather is formed by two pipes welded together to define an inner volume in a general D shape. The pipe of the upright leg of the D shape contains, at its upper end, an annular final filter element through which compressed gas flows to a clear compressed gas outlet at the top end of the upright leg. The lower zone formed by the lower end of the upright leg and the lateral branch pipe therefrom provides a sump for collection of oil for ultimate return to a compressor unit. The configuration of the disclosed separator vessel of U.S. Pat. No. 4,668,252 suffers from a number of practical disadvantages while still providing a more compact vessel than the conventional large pressure tank. Firstly, the vessel is formed by two pipe lengths which must be fabricated together by pressure resistant welds to provide the oil collection sump which add to overall manufacturing costs. Secondly, the upright configuration of the vessel with two relatively small volume upright passages leading to the final filter element provide an easy route for foaming oil to flow into contact with and thereby damage the final filter element. As a result, the compressor system would be required to operate with severely restricted oil volumes. Thirdly, because the filter element is housed within the upright leg of the vessel, it is necessarily axially very long to provide the required final filter flow area. This brings the filter element much closer to the oil level in the lower sump zone than would be desirable which exacerbates the aforementioned oil foaming problem. To be able to shorten the axial length of the filter element, it would be necessary to utilise pipes with much larger diameters which increases manufacturing costs.